Motor load distributing system for metal rolling mill



Ww w @di 26d@ .QW d@ P QN mw M Feb. 22, 1966 P. l.. MCMATH ETAL MOTORLOAD DISTRIBUTING SYSTEM FOR METAL ROLLING MILL Filed April 5, 1963 um mww n m ST W United States Patent() 3,237,071 MTR LOAD DlS'ERlBUTWGSYSTEM FR METAL ROLLING Mill.

Paul li... Meh/latin, Hales Corners, Wis., and Ralph E.

Perrault, Monrovia, Ealif., assignors, by mesne assignments, toAllis-Chalmers Manufacturing Company, Milwaukee, Wis.

Filed Apr. S, i963, Ser. No. 271,025 4 Claims. (Cl. S18-99) Thislinvention relates to a control for distributing the load on a group ofelectric motors. More specifically, this invention relates to a controlfor distributing the load on the motors that drive the work rolls in ametal rolling mill with automatic gauge control.

Some automatic gauge controls for metal rolling mills measure thethickness of the strip being rolled, compare the measured thickness witha reference thickness, and order any appropriate changes in the force ofthe work rolls on the strip. The reference thickness decreases fromstand to stand in the direction of rolling to cause each stand tocontribute part of the total reduction in the strip thickness. Since theload on a work roll drive motor depends on the reduction at its stand,the drive motors share the mill load according to the relative values ofthe reference thicknesses. The automatic gauge control at each standvaries the work r-oll force as various factors cause the gauge to differfrom the reference, and it gradually increases the work roll forceduring the rolling process as the strip cools and Ibecomes harder. Thisinvention is particularly concerned with the problem of keeping a`satisfactory distribution of the load on the Work roll drive motors.

One object of this invention is to sense when the load on the work rolldrive motor of one reducing stand is at a predetermined high level andto operate the reducing stand to shift some of this load to the nextstand. Another object of the invention is to sense when the next standis loaded at a predetermined high level and to prevent shifting the loadforward to the next stand in this situation.

Another object of this invention is to sense the load on the last standwith automatic gauge control and to perate the preceding reducing standsto shift the load backward before the last stand reaches a preset highload level. Another object of the invention is to prevent shifting theload backwards to stands that are already heavily loaded.

Another object of the invention is to provide a warning to the milloperator whenever all of the stands with automatic gauge control -havereached a level at which it is undesirable to shift the load backwardfrom stand to stand and to prevent further forward shift.

Another object of the invention is to provide a warning to the milloperator when none of the stands can accept additional load `from thelast stand, and the load on the last stand has increased to a secondpreset high level.

The drawing and the detailed description of the invention will suggestother objects and advantages of this control.

The control of this invention senses two load conditions at each millstand that has automatic gauge control. The rst level warns that theload is becoming high but the motors still have capacity to drive therolls as the roll force is increased. The second level indicates thatthe load should not be increased farther. For example, the second levelmay be set just below the level that protective devices would trip outthe work roll drive motor. In response to a signal indicating the secondlevel, the control operates the work roll positioning mechanisrn toreduce the roll force until the load falls to the ice rst level. Thereduction in load-at this stand must be made up at the following standsif the material is to have the desired thickness, and the automaticgauge controls cause the load to be shifted aheadv from the stand thatis partially unloaded. When the vload on the mill increases so much thatthe last stand reaches the first load level, the control shifts the loadbackwards, in a preset sequence, to any stand that is not alreadyoperating at the lirst level. ln this way the control keeps any standfrom becoming overloaded, and it assures that every stand will be highlyloaded before the last stand is operated by its automatic gauge controlabove the first load level.

ln the drawing, the single figure is a schematic of a rolling mill withautomatic gauge control and the control of this invention.

The mill and the automatic gauge control The mill that the drawingillustrates has three reducing stands lo which have automatic gaugecontrol. Stands l@ are suilixed a, b and c in the direction of rolling,and these sumxes are used to distinguish between equivalent componentsused at more than one reducing stand. Stands iti represent the iirst,next to the last, and last stands and illustrate intervening stands withautomatic gauge control. Other stands with or without gauge control (notshown) may be located in any position. Each stand i0 has Work rolls andbackup rolls ll. that are driven -by a motor l2 to pull a strip 13through the mill. A device ld `for each stand is controlled to positionthe work rolls il. and apply force through the work rolls on strip 1.3.Each stand l@ has a thickness measuring device (not shown) that producesa thickness signal l5. The automatic gauge control of each stand has ameans ld that compares gauge signal 15 with a reference 17 (combinedwith a reference biasing signal that will be described later) andproduces a thickness error signal 18.

In response to signal 18, roll positioning device 14 varies the yworkro-ll force to maintain the reference gauge. As will be explained later,the control of this invention biases the reference i7 to adjust the loadon motors.

The components of the mill and the automatic gauge control that havebeen described are well known and they have been described -suicientlyto suggest the `application of the control of this invention to varioustypes of mills and automatic controls.

The forward load shift The control of this invention includes for eachstand lila, Mb, and lite, a load sensing relay 2@ that produces a presetrst load level signal 2l and a load sensing relay 22 that produces apreset second level signal 23. Preferably, the relays 2t), 22 areadjustable by the mill operator so that signals 2l, 23 correspond to thecharacteristics of the associated stand lil. As will be explained, thesignals 21, 23 are used toindicate whether a stand should shift some ofits load to the other stands and whether the stand could accept part ofthe load from other stands. Stands lila and ltlb have identicalconiponents that operate in response to signals 2l, 23 to shift the loadforward. These components are shown in detail inside the dotted linesfor stand ltlb and shown by a 'box for stand lila. (Since the last standltc cannot shift its 'load forward, its control is different from t-hecontrol of the preceding stands lila, 10b.)

As the controls for stand 10b iilustrates, the `second level signal 23sets a device 25 such as a iiip-iiop to produce a signal 2d thatindicates that the motor has reached the second level. Device 25maintains output 26 until it is reset even though the load falls belowthe second level and signal 23 is removed. A reset signal .AND gate 29from energizing its output 32.

27 (the complement of signal 2l) is developed from first level signal 2lby means of a NOT gate 28 and is applied to the reset input of device 25to reset device 25 when the load falls below the first level.Preferably, signal 26 is applied to reduce the load on the stand only ifthe next stand is not at the second level. An AND gate 29 receivessignal 25, and it receives a signal 3th: that is derived from the secondlevel signal 23 of the last stand with automatic gauge control, ltlc, bya NOT gate 31 to indicate when the load of stand lldc is below thesecond level. AND gate 29 produces an `output 32 when the load on standllfib should be reduced to the first level and this action will notexcessively load the last stand c. The complementary output of deviceprovides a suitable signal 30h for controlling a corresponding AND gatein the box representmg part of the control of the preceding stand lila.

Signal 32 is transmitted to a device 33 that combines signal 32 and asignal that will be d-escribed later and produces a signal 34 thatindicates that the load on the stand should be changed. An integrator 35receives signal 34 and produces an output 36 that is combined withreference signal 17 in automatic gauge control device I6. Device 33` maycomprise the input circuitry of integrator 35. So long as device 25 isset and the Stand 10c is below its second level, signal 34 operatesintegrator 35 to change the reference bias signal 36.

Suppose that stand 10b is operating below the first level and that theload on its motor l2 increases sufficiently to actuate load sensingrelay 22 to set device 25 and energize output 26. If the last stand ltlcis -at level two, the absence of a signal at input 36C to AND gate 29prevents In this situation device 25 would maintain its output 26energized until the load on stand 10c is reduced below level two oruntil some other factor causes the load on stand 10b to fall below thefirst level. When both inputs 2d and C are energized, AND gate 29energizes output 32 and input 34]) of integrator 35b is energized in apolarity for integrator 35h to begin increasing reference bias signalSb. In response to the increase in reference bias signal 36h, rollpositioner I4b opens the work rolls lll of stand lltlb and therebyreduces the load on motor I2. When the load has been reduced below thefirst level, load sensing relay Ztb cooperates with NOI` gate 2S toenergize reset input 27 of device 25 and thereby deenergize input 34b ofintegrator 35h. Integrator 351; then maintains its output 36h at thelevel that reduced the load on the stand 1Gb to below the first level.After device 25 is reset, the automatic gauge control of stand 10b isfree to increase or decrease the Work roll force in response tovariations in thickness signal l5.

Preferably as the drawing indicates, components Ztl, Z2, 25, 28, 29, 33and 35 are well known static logic elements. If desired these componentsmay be made up of electromechanical load sensing relays 20, 22, a thirdrelay in device 25, and their contacts. Device 25 may comprise the thirdrelay with its coil connected to be energized by a pair of normally opencontacts on relay 22 (represented by signal 23) in parallel with theseries combination of a pair of normally closed contacts on relay 2t)(represented by NOT ga-te 28) and a normally open pair of contacts onthe relay of device 25. The relay of device 25 also operates a pair ofnormally open contacts represented by output 26 and a pair of normallyclosed contacts represented by output Stb. AND gate 29 may comprise thes-eries combination of a pair of normally open contacts alreadymentioned on the relay of device 25 and a pair of normally closedcontacts (represented by NOT gate 3l) on the second level relay 22C ofthe last stand 10c. Integrator 35 may comprise, for example, areversible motor connected to drive a potentiometer, an integratingamplifier, or a digital counter. Device 3.3 may comprise the input tointegrator 35.

The backward shift of the load The control that has been described foropening the work rolls to shift the load forward from stands 10a' and10b is not applied to the stand 10c because the strip I3 would leave themill over gauge. The control for the last stand ltlc responds to thefirst level signal 21C from load sensing relay Ztlc to operate othercomponents to shift the load backwards. These components are illustratedin the drawing by AND gates. The arrangement of these gates is intendedto present the functional relationship of the components in a verbalform and to suggest connections of contacts on the relays 2d, 22.Variations of this specific logic network will be apparent from wellknown design techniques.

An AND gate 4t) receives a first level signal Zic from the stand fdc andthe complement first level signal Zlb from stand ltlb and produces asignal 41 whenever the stand 10c is loaded to the first level and stand10b is not loaded to the first level. Signal 41 energizes input 34b ofintegrator 35b in a polarity to reduce reference bias signal 36b andcause work roll positioning device 14h to increase the roll force atstand 10b. Output 41 of AND gate 4d will remain energized until the Workroll force at stand 10b has increased sufficiently to bring the load onthe stand 10c below the first level or until the load on stand 10b hasincreased sufficiently to actuate load sensing relay Zflb and therebydeenergize input 271) to AND gate 40.

When both the stand 10c and stand lub are at the first level, thecontrol tries to increase the load on stand lfm. An AND gate 43 receivesythe first level signals 2lb and 21C from stands 10b and 10c andenergizes an output 44 whenever both stand 10b and stand libc' are atthe first level. Output 44 energizes one input of an AND gate 45 and acomplement first level signal 27a from stand lila energizes anotherinput of AND gate 45. When both stand 10b and stand we are at the firstlevel and stand 10a is below the first level, AND gate 45 energizes itsoutput 46 in a polarity to reduce reference bias signal 36a and therebyincrease the load on stand lila.

An AND gate 48 receives a first level signal 21a from stand 1Gb andsignal 44 from AND gate 43 and energizes an output 49 whenever thestands 10a, 10b, an-d 10C are at level one. Output 49 operates an alarmthat tells the mill operator that each stand is operating at the firstlevel. The mill operator may consider some corrective action notprovided by this control, or he may allow the mill to operate withoutchange since the motors l2 still have capacity for increased load up tothe second level.

Preferably, gates 40, 43, 45 and 48 comprise static logic devices. Ifdesired, the gates may comprise contacts on electromechanical relays 20,22. AND gate 4U may comprise the series combination of a pair ofnormally open contacts on the relay 20c of stand lfc and a pair ofnormally closed contacts (indicated by NOT gate 28) on the relay 2Gb ofstand llflb. AND gate 43 m-ay comprise a pair of normally open contactson each first level relay 24M), Zflc, of stands 10b, llttc. AND' gate 45may comprise the series combination of a pair of normally closedcontacts on the relay 20a of stand lila, a pair of normally opencontacts on relay Ztlb of stand 10b, and a pair of normally opencontacts on the relay 20c of the stand lila'. AND gate 4S may comprisethe series cornbination of a pair of normally open contacts on eachrelay 20 of stands 10a, 10b, llflc.

The control of this invention and the automatic gauge control willmaintain the desired gauge without overloading any of the motors untilthe load on the last stand in the Aautomatic gauge control reaches thesecond level. Output 23 of the second level sensing relay 22 of the lastgauge controlling stand operates an alarm that tells the mill operatorthat this stand is operating near its maximum load. The operator mayelect to let the mill run and to rely on safety devices to protect themotor, or he may elect other procedures not provided by this control.

The sequence that thas been described of shifting the load backwards inthe reverse order of the reducing stands is somewhat arbitrary and theAND gates 4), 43, 45 and 48 may be connected to shift the load backwardsin any desired sequence.

As the control has been described so far, the tirst level s-ignal isused for the two independent lfunctions of estabylishing the portion ofthe load that Jche control shifts forward .and establishing the level atwhich the stand is isolated from the backward shift of the load. Ifdesired, a stand (except the last stand with automatic gauge control)may be provided with two load responsive relays where the single relay lis illustrated. One would provide reset input signal 27 to limit theforward shift of the load and one would provide the complementarysignals 21 and Z7 to control the backward shift of the load.

This description of the invention will suggest to those skilled lin theart a variety of devices that rare suitable for the functional boxesshown in the drawing and variations in the relation of the componentswithin the spirit of the invention and the scope of the claims.

Having now particularly described and ascertained the nature of our saidinvention and the manner in which it is to be performed, we declare thatwhat we claim is:

1. A control for a selected -last stand and a plurality of precedingstands, all with automatic gauge control, in a metal rolling mill,comprising,

means connected to sense the work roll drive motor load of each of saidstands to produce a first signal for each of said preceding stands whenthe motor load is at or above a preset irst level and to produce asecond signal for each of said stands when the load is at or above .apreset second level,

flip-Hop means for each of said preceding stands connected to be set bysaid second signal 'and to be reset by the complement of said rst signalof the associated stand, means for each of said preceding standsconnected to respond to the output of the flip-op of the associatedstand and the complement of the second signal of the next stand in thedirection of rolling to produce a binary control signal, and

integrator means for each of said preceding stands connected to respondto the control signal of the associated stand and to operate on theautomatic gauge control to reduce the motor load -at the associatedstand to below said `first level after the load rises to the secondlevel. y2. A control for a selected last reducing stand and a pluralityof preceding stands, all with automatic gauge control, in a metalrolling mill, comprising,

means for each lof said stands connected to sense the load -on the -workroll drive motors and to produce a signal when the motor load at theassociated stand reaches a preset level, said load sensing means on eachof said preceding stands having a ip-ilop connected to Ibe set when themotor load reaches a preset relatively higher level and to be reset whenthe load reaches a relatively lower level, means for each of saidpreceding stands connected to respond to the signal of the associatedstand .and the complement of the signal from the next stand -in thedirection of rolling to produce a control signal, and

means responsive to said control signal to operate on the automaticgauge control of the -associated stand to reduce the load on theIassociated stand by a preset amount.

3. A control for -a selected last reducing stand and a plurality ofpreceding stands, all with automatic gauge control, in .a metal rollingmill, comprising,

load sensing means for each of said stands connected to sense the workroll drive motor load and to produce a iirst signal when the load risesto a rst preset level,

each said load sensing means for said preceding stands produces a secondsignal when the motor at the associated stand reaches a second levelthat is higher than the associated rst level,

means responsive to said first level signal .from said last stand and tothe complement of said :first level signal from a irst of said precedingstand when said last stand is at or above its rst level and said rstpreceding stand is below its yfirst level, and

means responsive to the complement of said iirst signal of a second ofsaid preceding stands and said rst signals of said rst and last standsto shi-ft part of the load on said last stand to said second precedingstand when said -irst preceding stand and said last stand are at orabove said iirst level Iand said second preceding stand is below saidfirst level,

means for each said preceding stand for operating on the automatic gaugecontrol of the associated stand to shift the load forward from theassociated stand when its load reaches its second level, said means -forshifting the load forward comprising a flip-flop that is connected to beset by `the associated second signal and to be reset by the comple--ment of the .associated first signal, and

an integrator connected to receive Ian output of said flip-flop toincrease the reference thickness at the associated stand until the loadat the associated stand has fallen below its rst level.

4. A control according to claim 3 in which said means that operates toshift the load forward includes -a logic gate for each of said precedingstands, each gate being connected to receive an output from the Hip-flopof the associated stand and each except the next to said last beingconnected to receive a complementary signal from the flip-flop of thenext preceding stand in the direction of rolling, the flip-flop 4of saidnext to the last stand being connected to receive the complement of thesecond level signal of said last stand, whereby each said gate energizesthe associated integrator only when the associated stand is at or aboveits second level and the next stand in the direction of rolling is notat its second level or operating to shift the load forward.

References Cited by the Examiner UNITED STATES PATENTS 1,969,536 8/1934Winnie. 2,752,545 `6/ 1956 Halter 3118-7 2,933,626 4/1960 Giboney et al.318-6 X 2,972,268 2/1961 Wallace et al 318-6 X `2,972,269 2/ 1961Wallace et al. 3118-6 X 3,078,746 2/1963 Dirth et al. '318-6 X 3,160,80212/1964 Obell 318-7 FOREIGN PATENTS 1,222,878 6/ 1960 France.

438,690 111/ 1935 Great Britain. 716,488 l-2/ 1941 Germany.

ORI'S L. RADER, Primary Examiner.

1. A CONTROL FOR A SELECTED LAST STAND AND A PLURALITY OF PRECEDINGSTANDS, ALL WITH AUTOMATIC GAUGE CONTROL, IN A METAL ROLLING MILL,COMPRISING, MEANS CONNECTED TO SENSE THE WORK ROLL DRIVE MOTOR LOAD OFEACH OF SAID STANDS TO PRODUCE A FIRST SIGNAL FOR EACH OF SAID PRECEDINGSTANDS WHEN THE MOTOR LOAD IS AT OR ABOVE A PRESET FIRST LEVEL AND TOPRODUCE A SECOND SIGNAL FOR EACH OF SAID STANDS WHEN THE LOAD IS AT ORABOVE A PRESET SECOND LEVEL, FLIP-FLOP MEANS FOR EACH OF SAID PRECEDINGSTANDS CONNECTED TO BE SET BY SAID SECOND SIGNAL AND TO BE RESET BY THECOMPLEMENT OF SAID FIRST SIGNAL OF THE ASSOCIATED STAND, MEANS FOR EACHOF SAID PERCEDING STANDS CONNECTED TO RESPOND TO THE OUPUT OF THEFLIP-FLOP OF THE ASSOCIATED STAND AND THE COMPLEMENT OF THE SECONDSIGNAL OF THE NEXT STAND IN THE DIRECTION OF ROLLING TO PRODUCE A BINARYCONTROL SIGNAL, AND INTEGRATOR MEANS FOR EACH OF SAID PRECEDING STANDSCONNECTED TO RESPOND TO THE CONTROL SIGNAL OF THE ASSOCIATED STAND ANDTO OPERATE ON THE AUTOMATIC GAUGE CONTROL TO REDUCE THE MOTOR LOAD ATTHE ASSOCIATED STAND TO BELOW SAID FIRST LEVEL AFTER THE LOAD RISES TOTHE SECOND LEVEL.